This invention relates to an acceleration-slippage controller for reducing slippage that occurs between the driven wheel and the road surface during vehicle acceleration.
An example of the prior-art controllers for reducing the acceleration slippage is disclosed in Japanese Published Unexamined Patent Application S61-85248. When acceleration slippage occurs at a driven wheel, this controller executes both the throttle valve control and the brake control to slow the revolution of the driven wheel. This device has been contrived because the throttle valve control and the brake control are individually inadequate because of the respective shortcomings set forth below:
(1) The throttle valve control cannot quickly lower the output torque of the engine to slow the driven wheel's revolution.
(2) The brake control can quickly reduce the driven wheel's revolution. However, it shortens the lifetime of the braking device because the brake control must reduce the driven wheel's revolution against the driving torque of the engine, thus applying a considerable load to the braking device.
When the throttle valve control and the brake control are started together as in the discussed prior art, each compensates for the other's shortcoming, thus efficiently reducing the acceleration slippage at the driven wheel.
In the prior-art controller described above, the throttle valve control and the brake control work independently of each other, but they influence each other. Specifically, both the brake control and the throttle control depend on the driven-wheel speed, and the efficiency of the brake control in reducing the driven-wheel speed is about ten times greater than that of the throttle control. As a result, the driven-wheel speed on which the throttle control depends is greatly influenced by the brake control, that is, the throttle opening is greatly influenced by the brake force, resulting in hunting. This lengthens the time necessary to control the acceleration slippage, which is contrary to the reason for combining the controls in the first place.
To solve this problem, another controller has been proposed where the reference value VB of the driven-wheel speed for the brake control is preset greater than the reference value VS for the throttle valve control. The brake control is executed only when severe acceleration slippage occurs at the driven wheel, to minimize the period of combined control.
The problem described above, however, remains as long as the two controls are executed together. Further, since the brake control is not executed until the driven-wheel speed exceeds the higher reference value VB, the responsiveness of the acceleration-slippage control deteriorates when the driven-wheel speed approaches the lower reference value VS.